You might be able to spot a psychopath by their eyes

Lead author, Dr. Dan Burley, from Cardiff University’s School of Psychology, said: “Our findings provide physical evidence of an emotional deficit common to psychopathic offenders.

“The pupil has long been known to be an indicator of a person’s arousal. Card sharks have learnt to look carefully at the eyes of their opponents to gauge if they have a great hand, and many an astute salesperson knows to up their price if your eyes reveal your excitement at their product. Likewise, the pupil usually dilates when an image shocks or scares us. The fact that this normal physiological response to threat is reduced in psychopathic offenders provides us with an obvious physical marker for this condition.”